5E3 amp output power question

[Andrei_T]

Hi, I have a 5E3 type amp on the bench, that the owner sais comes too soon into distortion. I have measured the output power and it has 20V peak to peak into an 8 Ohm load before clipping which results in 6.3 Wrms power output which seems much less then the claimed 15W. I measured all voltages and they seem OK. 315V B+, 250 Ohms cathode resistor with 18V voltage drop whitch means 33mA on each 6V6. Tried SS diodes as rectifiers and still the same output power... Is this normal output power?
Can anyone confirm the peak to peak output voltage before clipping on this type of amp?

[guitarmike2107]

Are you measuring into a resistive load?

[Andrei_T]

Yes, as I have written, into an 8 Ohm load.

[guitarmike2107]

I was just checking that you were not measuring it into a speaker "8 ohm load"

[Andrei_T]

No speaker it's a big resistor 8 Ohm 200W

[MWJB]

315vdc B+ is low for a "5E3", but you should still have more than 6W RMS. When you say "5E3" type amp, is it a proven layout, or just someone's idea of a 5E3?

It would still be usefull to know dc voltages, even if they appear "normal". Best to measure plate current rather that try and deduce it, not that there initially seems to be anything amiss here.

Is the AC output symmetrical at each end of the OT primary, have you checked the value of the 56K plate & cathode load resistors in the PI? You don't want a significant mismatch here.

Fender suggest 10VAC RMS at the speaker (12.5W), but their version runs much more voltage than the amp you have, so scale your expectation accordingly.

[guitarmike2107]

I missed the low voltage. but that would account for a largish power drop, maybe down to 7-8 watts. You cant really compare it unless you get the voltage up.

I just posted this in another topic

[Andrei_T]

Thanks for your replyes. It is a Collins Amplification 5e3 type amp and I think you're right that the low power output is due to the lower B+ in this amp. Thank you for your help.

[pdf64]

'Tried SS diodes as rectifiers and still the same output power'
Could you double check that?
As the B+ should have risen ~50Vdc, with the resultant increase in output power.

[MWJB]

Agreed, with 315vdc and a 5Y3 (NOS) a SS rectifier (diodes only, not a copper cap) should have brought your B+ up to typical/high 5E3 B+ voltages.

Andrei, refit the diodes & compare AC & dc voltages with the 57 Deluxe schematic at Fender.com.

[Twist]

Does the output tranny have the right impedance ratio for a pair of 6V6's into an 8 ohm load? I'm assuming this is a project amp.

[ThermionicScott]

Does the output tranny have the right impedance ratio for a pair of 6V6's into an 8 ohm load? I'm assuming this is a project amp.

That's a good question. The iron could be wrong, or if it has multiple secondary taps, the wrong one might have been used.

Technically, the Deluxe Reverb-style OT included in many 5e3 kits has the wrong primary impedance, but it seems to put out enough power and sound good enough for most users.

-Scott